Recently, proposed has been a method for producing a toner, which include melting a thermoplastic resin and bringing the melt resin into contact with a compressive fluid, followed by mixing the melt resin and the compressive fluid by a conventional type of a static mixer, to reduce a viscosity of the melt resin, and decompress the obtained mixture to expand, to thereby produce a toner (see PTL 1). According to this proposed method, a toner can be produced with maintaining energy cost low.
In the case where fluids each having different viscosities, such as a melt resin and liquid carbon oxide, are mixed using a static mixer like in the case of PTL 1, however, it is difficult to homogeneously mix the both fluids together. As for the static mixer, known is a static mixer having a mixing element in a tube-shaped housing. The mixing element does not have a moving part, and has a plurality of baffle plates, which are aligned along the axial direction with the tube axis as a center. In the static mixer, a fluid is mixed by being split, turned about, and turned over by the mixing element provided in the tube, as the fluid go through inside the tube-shaped housing. As for another type of a static mixer, known is a mixer, in which, as a mixing element, a large number of honeycomb-shaped plates composed of small polygonal rooms are aligned to overlap each other.
In such static mixer, a fluid is mixed by being dispersed, turned over, and spin around, as the fluid sequentially moves through the small rooms in the tube from the centric part of the tube to the outer side, and the outer side to the centric part of the tube.
However, when a thermoplastic resin, which is a highly viscous fluid, and a compressive fluid, which is a low viscous fluid, are passed through in the static mixer, the compressive fluid is passed through a space between the mixing element and the tube-shaped element, without receiving a mixing action from the mixing element. As a result, the both fluids may not be homogeneously mixed. Therefore, the compressive fluid is not sufficiently dissolved in the thermoplastic resin, so that a viscosity of the thermoplastic resin is not sufficiently reduced. Even when the resulting mixture is expanded by decompression, diameters of obtained particles become large, e.g., several hundreds micrometers to several millimeters, and a particle size distribution of the particles becomes wide due to fusion of the particles, and generated fibrous products. Accordingly, there is a problem that it is difficult to produce a large amount of uniform particles having small particle diameters.
There are countermeasures for the aforementioned mixing failure, such as giving a mixing element a complex structure, and elongating a mixer. However, these countermeasures are not effective method for preventing the compressive fluid, which is a low viscous fluid, from passing through, and therefore there are problems, such as an increase in pressure loss during mixing, an enlarged device, and an increase in washing effort.
Accordingly, there is a need for providing a production method for producing particles having a narrow particle size distribution and having small particle diameters, in which a thermoplastic resin, which is a high viscous fluid, and a compressive fluid, which is a low viscous fluid, are brought into contact with each other to produce a melt, and jetting the melt to form particles.